The invention relates generally to wireless communication systems for isolated devices, and more particularly to electromagnetic signalling and telemetry systems for physiological implants and the like.
Externally applied oscillating magnetic fields have been used before with implanted devices. Early inductive cardiac pacers employed externally generated electromagnetic energy directly as a power source. A coil inside the implant operated as a secondary transformer winding and was interconnected with the stimulating electrodes. More recently, implanted stimulators with rechargeable (e.g., nickel cadmium) batteries have used magnetic transmission to couple energy into a secondary winding in the implant to energize a recharging circuit having suitable rectifier circuitry. Miniature reed switches have been utilized before for implant communications. They appear to have been first used to allow the patient to convert from standby or demand mode to fixed rate pacing with an external magnet. Later, with the advent of programmable stimulators, reed switches were rapidly cycled by magnetic pulse transmission to operate pulse parameter selection circuitry inside the implant. Systems analogous to conventional two-way radio frequency (RF) and optical communication system have also been proposed.
The increasing versatility of implanted stimulators demands more complex programming capabilities. While various systems for transmitting data into the implant have been proposed, there is a parallel need to develop compatible telemetry systems for signalling out of the implant. However, the austere energy budget constraints imposed by long life, battery operated implants rule out conventional transmitters and analogous systems.